Epistemic status: I am not a doctor. This is based on a combination of the most rigorous medical lit searches I could do over several hours, and individual reports that may or may not be based on anything. Wherever possible I’ve provided links to my sources so you can form your own opinions.

This is based on my best knowledge right now. I could be missing things, or new information could come to light, in which case I will update this as quickly as possible (and appreciate holes being pointed out).

Before you get sick

Uncontroversial

1. Buy zinc lozenges (acetate or gluconate)
2. Buy electrolytes in some form.
3. Buy a thermometer.
1. Take your temperature several times over several days to get a sense of your baseline.
4. Buy a pulse oximeter if you can’t trust your subjective sense of “am I getting enough air?”, e.g. if you get panic attacks.
1. ETA 4/22/20: Looks like at least some subset of people can be dangerously oxygen-impaired without noticing, making this a much better idea..
2. Measure your oxygen saturation several times over several days to get a sense of your baseline.
5. Look for COVID-19 related drug trials in your area, so you will have the information if you need to join one later
6. Form care arrangements (for yourself, pets, kids, parents, etc) with people who will be able to follow through.
7. You’re already quarantined, right?
8. Buy gloves and masks for the person taking care of you (yeah, this is kind of aspirational at this point)
9. Buy something to bring down your fever (an antipyretic). France is recommending against NSAIDs and against ibuprofen in particular. I will be very surprised if that ends up being born out (and WHO agrees with me), but if you believe them, you’ll want acetaminophen. If you don’t, any NSAID will work
10. Buy pseudoephedrine (the real stuff, which is behind the counter in the US. Sudafed PE is useless).

Controversial

1. Research drugs you might like to take if you got sick. I am deliberately not linking to more information on this because nothing is sufficiently certain right now that I feel comfortable recommending it to people who haven’t done their own research.
2. Find a sketchy online pharmacy and buy drugs and medical equipment you feel confident self-administering.

At The First Sign of Illness

What are the signs?

That's an excellent question, but the more I research it the less confident I am in any particular answer. My eventual conclusions will be going up at this question, although right now I think the answer is going to be "feel sick? then maybe."

Uncontroversial

1. Start taking zinc lozenges (gluconate or acetate. The terrible taste and loss of sense of smell says it’s working, unless you already lost your sense of smell to COVID).
2. Set up your environment so it is easy to frequently drink small amounts of liquid, ideally with electrolytes.
3. Rest, rest, rest
4. Look for RCTs and drugs you might want to ask your doctor for, if you haven’t already.
5. Restrict contact with other members of your household. Even if you've already exposed them, dosage matters, and you can spare them as much exposure as you can.
6. Alert your care team. If anyone seems flakey, start looking around for new members.
7. Check in with your doctor. They probably can’t do anything, but maybe you’ll get a test out of it, and that’s useful to your friends.
8. Contact anyone you had contact with to warn them. Ask them to contact people they’ve contacted recently. Hopefully the number is small because you’ve been practicing good isolation.
9. Take pseudoephedrine if you have unpleasant sinus pressure.

Controversial

1. Do any research you told yourself you would do between buying sketchy drugs or medical equipment from sketchy online retailers and actually using them.
2. Start any drugs acquired from sketchy online pharmacies that you have researched thoroughly enough to be willing to accept the consequences of your choice.

While Continuing to be Sick

1. Continue to rest and hydrate, with electrolytes.
2. Monitor your temperature. Let your fever play out unless it’s over Nº, at which point it’s legit dangerous to you and you should take the antipyretic you bought.
1. I went looking for an exact value for N, but couldn’t find good studies on it, especially in adults. I was taught 103ºF, some people say 104ºF, that’s probably the range.
3. (Optional) monitor your oxygen saturation.
4. Continue to eschew human contact as much as possible.

When should I seek medical attention?

This depends in part on how functional your medical system is. If you’re in a place where you can get a drive by test and your doctor will order you experimental drugs over the phone, maybe do that. If you’re in the US, I don’t expect calling a PCP to do much even if you have one, which many people don’t. So your choice is “When do I go to the hospital?” keeping in mind that the hospital is well over capacity and that if you don’t have COVID going in, you’re likely to catch it there.

So I personally wouldn’t go to a hospital unless I clearly needed something I couldn’t get at home, which basically means oxygen or whatever they do when your fever is dangerously high for too long, which means “when I struggle to breathe” or “when my temperature is over Nº and antipyretics won’t bring it down”.

In a few places above I advise you to call your primary care physician, knowing full well many people don’t have one and that there’s not a lot they can do for COVID. That’s more ass-covering and future-proofing than anything; I’d feel really bad if it turned out they could do something and you missed out because I told you not to.

Take chloroquine or hydroxychloroquine along with zinc ASAP (so you can avoid being hospitalized). ETA: Preferably after talking to your doctor about it. See references below for more details. If you didn't buy chloroquine/hydroxychloroquine ahead of time, beg your doctor for a prescription, or call doctors around you until you find someone willing to give you a prescription (because unlike China and South Korea, it doesn't seem to be part of the standard treatment for COVID-19 in the US).

• https://docs.google.com/document/d/e/2PACX-1vTi-g18ftNZUMRAj2SwRPodtscFio7bJ7GdNgbJAGbdfF67WuRJB3ZsidgpidB2eocFHAVjIL-7deJ7/pub
• https://www.youtube.com/watch?v=vE4_LsftNKM
• https://www.lesswrong.com/posts/un2fgBad4uqqwm9sH/is-this-info-on-zinc-lozenges-accurate
• https://www.connexionfrance.com/French-news/French-researcher-in-Marseille-posts-successful-Covid-19-coronavirus-drug-trial-results

ETA: Some relevant information from the CDC:

Based upon limited in-vitro and anecdotal data, chloroquine or hydroxychloroquine are currently recommended for treatment of hospitalized COVID-19 patients in several countries. Both chloroquine and hydroxychloroquine have known safety profiles with the main concerns being cardiotoxicity (prolonged QT syndrome) with prolonged use in patients with hepatic or renal dysfunction and immunosuppression but have been reportedly well-tolerated in COVID-19 patients.

[...] Hydroxychloroquine and azithromycin are associated with QT prolongation and caution is advised when considering these drugs in patients with chronic medical conditions (e.g. renal failure, hepatic disease) or who are receiving medications that might interact to cause arrythmias.

I read a lot of recommendations for electrolytes but found all of the explanations kind of vague, so I did 2 hours of digging (plus more research from Eli Tyre). This is what I found

What are electrolytes?

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. When applied to humans and health, it typically refers to sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), and is used for nerve signals and maintaining the right osmotic pressure in cells.

How does illness affect electrolytes?

Electrolytes are lost in sweat, including from fevers, environmental heat, and exercise. They can also be lost through diarrhea and vomiting- a big problem with bulimia.

Additionally, too much fluid can throw your electrolyte balance off, so if you’re following the advice to hydrate without taking electrolytes, you can make things worse.

What’s so bad about low electrolytes?

Your nerves will be worse at firing, leading to cramps, mental issues, and cardiac issues.

In extreme cases it can lead to spasms of the muscles in the throat (leading to difficulty breathing), stiffening and spasms of muscles (tetany), seizures, abnormal heart rhythms, and kidney failure (hypocalcemia, hypoatremia, hypokalemia). But you’re not going to let it get that far.

More speculatively, because calcium-based signalling is a key component in immune response activation, low calcium may weaken your immune system.

How speculative is this?

Not. Electrolytes are part of the standard routine in hospitals for COVID-19 and fevers in general.

Can I hurt myself with this?

Yes, but not easily. There is a level at which too much of any electrolyte is bad for you. My experience and the experience of many people I know is that you can tell by taste- electrolyte-enhanced water tastes amazing when you need them and unpleasantly salty when you don’t. Also barring certain specific problems like hypothyroidism, your body is pretty good at evening out your electrolytes as long as you give it the raw materials and time, so this is another reason to space out your fluid consumption.

The theory seems sound, what about the practice?

I looked for RCTs of electrolyte supplementation vs. not, but what I found was mostly studies of different types of rehydration therapies, always in children, and most for diarrhea induced imbalances rather than fever. The best I found was this meta-review showing isotonic IV fluid led to low sodium less often than low sodium IV fluid did

If you’re curious about the pediatric diarrhea studies...

• Should you include zinc?
• Glucose versus amylase resistant starch
• Oral vs IV

How much do I need and when do I need it?

The literature was not very forthcoming on this, and I’m not a great person to ask because I put salt in my water by default. My folk wisdom is to add it to your water that you should also be drinking to taste.

Thanks to Eli Tyre for help with the research for this comment.

EDIT: Changed blood oxygen numbers thanks to Jay Molstad Comment

What I would do if I had COVID-19? ( I am NOT a medical professional)

Ok. So you're sick. Maybe you have a fever and a bit of a cough. This may be COVID-19 and this may be something else like a seasonal flu. Even if you have COVID-19 the most likely outcome is that the symptoms are mild enough that you can deal with them at home. The South Korean Health Minister says 10%, so 90% you recover at home.

• Dealing with mild symptoms at home:
• Rest
• You shouldn't be doing anything strenuous. Just let your body fight off the virus. Maybe enjoy some shows or video games while you're at it.
• Keep drinking fluids
• Staying hydrated is important generally, but especially important when you're sick and may not be drinking and eating regularly. I would do this by drinking water, tea, and drinks made from electrolyte powders. Do make sure you're getting electrolytes somehow (LW discussion of electorlytes).
• Ask someone to check in with you regularly in case you do get worse.
• A housemate or a friend could message you to check in every day or two. Being sick sucks and possibly your judgement is impaired by a fever. If you and your friend are comfortable with it you can offload the decision making on when you should be worried enough to go to the hospital.
• There is some discussion of using chloroquine and/or zinc. I have not looked deeply into this. My immediate thoughts here are zinc seems low cost to take and chloroquine seems high cost to take.

• When should I go to the hospital?
• I'm going to write what I'd be looking for, but ultimately you must make your own decision. I am not a medical professional.
• Blood Oxygen Levels
• Maybe you got a pulse oximeter.
• Normal blood oxygen levels are 90-95%, but can be lower if you have other factors like sleep apnea.
• The WHO has been recommending to doctors to start giving oxygen therapy if the blood oxygen levels fall below 90%
• Based on Jay Molstad's comment below I would probably head to a hospital if my blood oxygen was below 90% and I was having trouble breathing or below 85% with or without trouble breathing.
• Note, you may have blood oxygen at a lower than normal range
• Shortness of Breath/Difficulty Breathing
• If you are having short painful breaths or having trouble breathing.
• Fever above a certain point.
• Sites vary here. Mayo Clinic says if the fever is above 103oF consistently or above 102oF for more than 3 days. This other site says 104oF and above is dangerous and you should seek immediate medical attention at 106.7oF
• It may take a few days before you know if you're going to have severe symptoms. For hospitalized patients these were some of the timelines observed.
• from first symptom to → Dyspnea (Shortness of breath) = 5.0 days
• from first symptom to → Hospital admission = **7.0 days*

• Maybe hospitals are overloaded.
• Measures like the shelter in place order in the bay area will help a lot with decreasing the load on hospitals, but it's still possible we end up with a peak at some point.
• You may want to try to get in anyway. If you're experiencing severe symptoms and have been turned away from a hospital you may want to try some things on your own.
• Some people have been buying oxygen concentrators. If your blood oxygen falls below ___ or you are having a difficult time breathing. Using one or seeing if a friend has one may be helpful. I want to note again I am not a medical professional. Oxygen toxicity is a thing so it's not like using an oxygen concentrator is risk free.
• If I had an oxygen concentrator and a pulse oximeter I would consider starting at a low flow rate and slowly increasing until my blood oxygen levels were above 90%, but being careful not to continue oxygen therapy if my levels returned to normal (90-95%, could be lower if you have other factors like sleep apnea).
• WHO recommendations to clinicians were.
• Start at 5 L/min and titrate flow rates to reach target SpO2≥90% in non-pregnant adults and SpO2≥92-95 % in pregnant patients.
• It’s unclear to me what concentration of oxygen they were using.

Take zinc at the first symptom.

Other people (Scott, PhilH, knzhou Cochrane Review) have gone into the science before and I don't have much to add to their research, but here's my adaptation for COVID-19 in particular.

My synthesis:

• The method of action is zinc ions attaching to your throat. So pills are useless. It has to be a lozenge.
• This implies that zinc is only helpful with infections of the throat, not nose or lungs. According to a source I can't find because I read it before starting the links DB, COVID-19 often starts in the upper respiratory track and becomes dangerous when it moves into the lungs. If that's true, a good zinc lozenge might inhibit COVID-19 from turning serious even if it can't prevent infection entirely (note that under this model you would still be contagious and should take appropriate precautions).
• Chris Masterjohn claims only zinc-gluconate and -acetate work. I don't know if this is true, but the only studies I found used gluconate and acetate, so it seems wise to prefer them.
• I need to stop chewing my lozenges to make the process faster.
• I hope you already bought the right kind because it's all sold out right now.

Caveats:

• "A cold" can be caused by coronaviruses, rhinoviruses, or other. None of the studies I skimmed tried to different between causes. It's possible that zinc works amazing for rhinoviruses but does nothing for coronaviruses, or is amazing for some coronaviruses but not SARS-CoV-2.
• The loss of sense of taste and smell says it's working.

Should I take zinc prophylactically?

My first-principles, completely unverified guess is that if you take zinc all the time your body will adapt and it will become less useful. Also you will lose your sense of smell. I'm not taking it while in isolation, but I definitely would if I was a medic or grocery clerk right now.

Listing / summarizing some things I've seen elsewhere:

This general summary post by Sarah Constantin: https://srconstantin.github.io/2020/03/27/home-care-mild-COVID19.html

A post by SC specifically on "non-invasive ventilation", meaning CPAP and BiPAP machines (which some people may already have at home), with positive conclusions: https://srconstantin.github.io/2020/03/20/non-invasive-ventilation.html

A document by Matt Bell with information about chloroquine phosphate / hydroxychloroquine: https://docs.google.com/document/d/160RKDODAa-MTORfAqbuc25V8WDkLjqj4itMDyzBTpcc/

One of the most intriguing things I saw was about "proning": https://emcrit.org/pulmcrit/proning-nonintubated/

The author of that post is Josh Farkas, a pulmonologist (i.e. lung specialist) and assistant professor of critical care and pulmonary disease (i.e. lung disease.)

"Prone" here means a face-down lying position, the opposite of "supine" which means face-up. The author says "Typically we prone intubated patients." From context, I am reading "we" to mean his hospital / department, and "prone" to mean "rotate into the prone position for 6-18 hours per day." The commonality of this practice seems to vary among hospitals.

The post, however, is a discussion of proning for awake, non-intubated patients, and concludes that it appears safe and effective. There is a lot of uncertainty around how effective it is, but it looks to me like, if you have pneumonia and hospital treatment is not available to you, there is some evidence that -- perhaps counterintuitively -- you will breathe better lying on your belly, vs. on your back.

(The main counterpoint I have seen to this is that frequently moving around and changing positions is best. I can't tell whether the post is largely about patients who are too out-of-it to do that. I have seen it suggested that, if you're able, sitting up is better than lying down (I have no cite handy for this.) There seems to be overall agreement, at least, on this one point: lying stationary on your back for long periods of time is NOT good when you have lung problems.)

Idea I saw someone float:

If [a COVID-19] case becomes severe & ventilator access is limited, postural drainage is a thing I would be trying (seems low-cost & fits my models about what sort of thing should help). https://www.healthline.com/health/postural-drainage

Relatedly, if you're showing COVID-19 symptoms, I think I would recommend that you start lying on your chest if you can sleep and rest well in that position, using pillows for support as needed. I base this on an NY doctor working in a non-ICU COVID-19 unit who says:

Proning [i.e., having patients lay on their stomach] is now standard in our ICU and I tried hard to get my sicker patients to do it too to head off intubation. [...]

https://twitter.com/SepsisUK/status/1243236007346163712 [...]

[in reply to "Is proning something we can do at home to help with milder symptoms? My brother is short of breath but not at ICU level, should he try this?":]

Yes, can’t hurt, likely help

I only looked at these studies briefly, but they suggest that ARDS patients benefit from lying on their stomach:

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4848155/
• https://www.atsjournals.org/doi/pdf/10.1164/rccm.202003-0527LE

Like Elizabeth, I remember reading somewhere that COVID-19 often starts in the upper respiratory track and becomes dangerous when it moves into the lungs. In line with that, one idea is to try to control the illness in the upper respiratory tract through sinus rinse/nasal irrigation (be sure to sterilize the water first). I haven't done much nasal irrigation, but I've found gargling with warm salt water to be really helpful for colds. This study found that simply gargling water for 15 seconds 3 times a day reduced upper respiratory tract infections by 36%! Breathing in steam or making use of a humidifier might also be helpful.

This pdf was linked from the 80K podcast. There are treatment instructions starting on page 8. There's also a section on what Traditional Chinese Medicine says you should do :P

There's also a thread on the slatestarcodex subreddit on what to do if you have a severe case and there's no room in the hospital. Another thread on that sub.

Find an RCT for COVID-19 treatment. This seems like a good compromise between "buy drugs from a sketchy foreign pharmacy and base dosage on a handful of papers" and "I dunno, my GP seems pretty on the ball".

One place I have found to find RCTs is https://clinicaltrials.gov/ . Normally I would verify the details of how to join but I assume they are busy right now. If you do try this, please report back.

Agree with the Vitamin D, C, and zinc. Also take nicotinamide riboside (a B3 variant) to raise PARP10 levels. (Recent paper on this):

https://www.biorxiv.org/content/10.1101/2020.04.17.047480v2

And don't forget to stagger around the neighborhood biting everyone... millions of movie fans have been waiting for this for decades.