Mixing over-the-counter medicine and alcohol is one of those things you know you shouldn’t do, yet sometimes life gets in the way. Maybe you popped a Tylenol to beat a midday headache and then got invited out to drinks, or allergy season hit and you’ve been taking Claritin for a month straight.

Cutting out alcohol seems extreme, so we checked with pharmacists and doctors to see if it’s OK to have a drink or two while taking over-the-counter medicine. While none wholeheartedly recommend it (and all said you should check with a pharmacist if you have any questions or preexisting conditions), for the completely healthy 20-something, here are some things to keep in mind.

1. Ibuprofen

Pain relievers like Aleve, Motrin, and Advil all fall in the category of nonsteroidal anti-inflammatory drugs (NSAIDs). They work by blocking the enzymes that cause pain and inflammation, making them a great fix for your standard aches and pains. These guys are lightly irritating to the stomach lining, so the addition of enough alcohol—another irritant—can lead to trouble.Game plan: If you just took Advil at lunch, you should be fine to drink at happy hour, says Margo Farber, a pharmacist and the director of the Drug Information Services at the University of Michigan Health System. But if you’re a chronic ibuprofen user (popping pills multiple times a day), then try to limit yourself to one or two drinks because these pain relievers likely already have your stomach irritated. And always try to have a meal beforehand to create a buffer in the stomach, says Marcus Reidenberg, M.D., professor emeritus of pharmacology at Weill Cornell Medical College.Watch out for: If you have more than two drinks, you may experience gastritis (which feels like nausea or indigestion) as a “natural stop” from your stomach, Farber says. Basically your stomach is sending the message that it’s not OK, so put down the drink and go home. Gastritis isn’t a huge cause for concern on its own, but ignoring it and adding more alcohol to the mix could lead to an ulcer and gastric bleeding, Reidenberg says.

2. Acetaminophen

Tylenol and the other medicines in the acetaminophen family seem to provide the same relief as ibuprofen, but there are a few key differences in how the two drugs interact with your body. When Tylenol is digested, a small portion—about 1 percent—is toxic to the liver. If you’re following the proper dosage, you shouldn’t run into any trouble. But when alcohol comes into play, an enzyme causes the toxicity level to rise to 4 or 5 percent, throwing your liver into the danger zone.Game plan: Timing plays a big role in your risk factor. Avoid double-fisting alcohol and any medicine, and the more you’ve had of one, the longer you should wait before having the other. So if you took a single Tylenol at lunch and wanted a single glass of wine at dinner, you should be in the clear, says Laura Knockel, a pharmacist and assistant professor at the University of Iowa College of Pharmacy. Watch out for: Most people run into issues when trying to cure a hangover. The classic situation: You’ve been drinking a lot over the weekend, stop Sunday night, and then takes a few doses of Tylenol the next morning. While you may feel sober, that doesn’t mean you’re in the clear—that’s actually when your liver is most in danger, Reidenberg says, because the enzyme that turns Tylenol toxic is still kicking around. There’s the potential that you’re playing with fire, but there’s no telltale symptom to know. So while the damage isn’t always life-threatening, it’s better to err on the side of caution, especially if you have an alternative, Farber says.

3. Antihistamines

These OTC drugs fall into two categories: first generation and second generation. First-generation drugs (like Benadryl) make you sleepy, while second-generation meds (like Claritin and Zyrtec) don’t have strong sedative properties. Game plan: If you’re taking a Claritin here and there throughout allergy season and not having any drowsiness, a drink or two won’t be a problem, Knockel says. But if you’re on a first-generation drug, which works by depressing your central nervous system, avoid drinking for at least eight to 12 hours after taking it, Farber says, otherwise you could wind up incredibly drowsy. Watch out for: If you’re feeling sleepy on a second-generation antihistamine, steer clear of the booze. The most extreme reaction possible would be respiratory depression (slower breathing), Knockel says, so if you’re more tired or woozier than normal after a few drinks, it’s time to ease up.

4. Multi-Symptom Medications

Like their name suggests, multi-symptom medications treat many ailments with one pill (cold and flu, cough and congestion). To do that, each medicine has many active ingredients. Some, like pseudoephedrine or phenylephrine (both decongestants), won’t cause any problems if you down a few beers afterward. But these medications also often contain things you have to watch out for when drinking, like acetaminophen or antihistamines. Game plan: Keep an eagle eye on the back of the box. Robitussin, for example, comes in multiple varieties, some with acetaminophen and some with antihistamines. Look for the main active ingredient (the one with the largest number of milligrams per dose) and determine if it will react poorly with alcohol. If the active ingredient is ibuprofen and your stomach hurts, or an antihistamine and you’re feeling extra drowsy, take note.Watch out for: NyQuil can already have up to 10 percent alcohol in it. In those situations, trust that that will do the job—no need to layer alcohol on top of it.

5. Antacids

If you’ve got an upset stomach or heartburn, you’re probably going to reach for an antacid—but the reason you’re feeling queasy could very well be from too much drinking. So luckily there’s little risk of mixing alcohol and Tums, but too much alcohol can also cancel out the stomach-healing properties of the antacid, rendering it virtually null.Game plan: Go forth and drink, but realize that you’re effectively undoing the medication. And if you’re feeling queasy from alcohol, chances are you’ll throw up, Tums or no Tums, Knockel says.Watch out for: The only exception to the rule is ranitidine, the active ingredient in Zantac. One study found that the blood alcohol content in people who drank after taking ranitidine rose 38 percent. That’s thanks to an enzyme interaction that inhibits the metabolism of alcohol (meaning that you get drunk faster, Farber says).Alcohol levels are increased in social drinkers receiving ranitidine. Arora S, Baraona E, Lieber CS. The American journal of gastroenterology, 2000, Feb.;95(1):0002-9270.”>Alcohol levels are increased in social drinkers receiving ranitidine. Arora S, Baraona E, Lieber CS. The American journal of gastroenterology, 2000, Feb.;95(1):0002-9270.The ranitidine study was relatively small, so it would have to be replicated on a larger scale to give solid data, but it’s still good to keep in mind if you’re planning on drinking, Knockel says.