how many days in a row is it safe to take advil and tylenol?

There is no single safe number of consecutive days for Advil or Tylenol that applies to everyone; the risk depends on your dose, your health, and how long you take them.

The evidence on ibuprofen (Advil) shows that risk rises with duration. A large UK study found that current NSAID use raised the risk of upper gastrointestinal bleeding about 5-fold overall, and that risk was higher with longer use and higher doses [1]. For ketorolac (a stronger NSAID), a retrospective study found that use beyond 5 days increased the risk of acute kidney failure, while use of 5 days or less did not [2]. A 2015 review notes that even short-term OTC use (1–7 days) can cause side effects, though ibuprofen at 1200 mg/day had a similar rate of significant adverse events (about 14%) as acetaminophen in a large tolerability study [3]. The risk is amplified if you have a history of ulcers, take blood thinners, or are dehydrated [1, 3].

The evidence on acetaminophen (Tylenol) focuses on the liver. A prospective study of 93 patients with acute liver failure found that those who took acetaminophen in a "therapeutic misadventure" (not a suicide attempt) took a mean of 4 grams per day for a mean of 4 days, and many were also heavy drinkers [4]. That study shows that even at doses within the labeled maximum (4 g/day), taking it for several days in a row can cause severe liver injury, especially if you drink alcohol [4]. The 2015 review notes that acetaminophen had a similar rate of significant adverse events as ibuprofen in short-term use [3].

My call: For a healthy adult with no risk factors, taking either drug for 3 days or fewer at the lowest effective dose is low-risk. Beyond that, the evidence does not define a safe limit. The risk of GI bleeding with ibuprofen and liver injury with acetaminophen both increase with consecutive days of use, and the data is too thin to say "X days is safe" for everyone. Confidence: moderate for the 3-day window; low for any longer period, because the studies that exist do not test the question of maximum safe consecutive days in a general population.