Anacin is the trade name of several analgesics manufactured by Insight Pharmaceuticals. Its flagship product contains aspirin and caffeine. It is primarily used for headache relief but it can also be used to calm minor pains due to sore throat, toothache, muscular aches, a cold, backache, arthritis, and menstrual cramps. 
Anacin was invented by William Milton Knight and was first estimated to be used in 1916 as stated in the patent. Anacin is one of the oldest brands of pain relievers in the United States, first beginning sales in the 1930s. Anacin's mascot at the time was Ana Anacin, who was found in a number of ads of this product.
It was originally sold by The Anacin Co. ("Pharmaceutical Chemists") in Chicago, Illinois. American Home Products, now known as Wyeth, purchased the manufacturing rights in 1930. Anacin was reportedly their "most popular product."  Insight Pharmaceuticals acquired the brand in 2003. In 2014, Prestige Brands signed an agreement with Insight to acquire the company; at that point it will become the largest acquisition to date.
Anacin is one of the earliest and best examples of a concerted television marketing campaign created for them in the late 1950s by Rosser Reeves of the Ted Bates ad agency. Many people remember the commercials advertising "tension producing" situations, and the "hammers in the head" advert with the slogan "Tension. Pressure. Pain."
A later Anacin advert (in 1962) featured a mother trying to assist her grown daughter with various chores, such as preparing a meal. "Don't you think it needs a little salt?", mother would say, only to have her nerve-racked daughter shout, "Mother, please, I'd rather do it myself!" As the mother wilted, the daughter would emote and rub her head, with her inner voice saying, "Control yourself! Sure, you're tired, you have a headache, but don't take it out on her!" Another commercial had a wife greeting her husband as he pulled into their driveway in his car; the husband responded by yelling "Helen, can't you keep Billy's bike out of the driveway?!?" These advertisement scenarios became popular and were parodied a number of times, including in the Allan Sherman song "Headaches," the 1966 film The Silencers and the 1980 film Airplane.
Anacin had a large advertisement behind the center field fence in Yankee Stadium from the 1950s through 1973, prior to the stadium's renovation in 1974 and 1975.
Early Anacin radio commercials appeared in radio shows and dramas of the 1940s and '50s. These "formulaic" commercials usually claimed that Anacin was being actively prescribed by doctors and dentists at the time, treated "headaches, neuritis and neuralgia," and that it contained "a combination of medically proven ingredients, like a doctor's prescription," without specifying those ingredients. Sometimes the announcer would mention that there were four active ingredients in Anacin, one of which was the medicine the consumer was already taking. The announcer then reminded the listener that Anacin was available "at any drug counter", and "come in handy (tin) boxes of 12 and 30, and economical family-size bottles of 50 and 100", usually spelling out its name at the end of the commercial: "A-N-A-C-I-N".
Anacin covers a family of pain relievers. There are six different formulations:
- Anacin Regular Strength - contains 400 mg ASA (aspirin) and 32 mg caffeine per tablet.
- Anacin Extra Strength - contains 500 mg ASA and 32 mg caffeine per tablet.
- Anacin Advanced - contains 250 mg acetaminophen (paracetamol), 250 mg ASA and 65 mg caffeine per tablet.
- Aspirin Free - contains 500 mg acetaminophen per tablet.
- Anacin 3 - acetaminophen
Anacin's side effects may include dizziness, heartburn, irritability, nausea, nervousness, rashes, hives, bloody stools, drowsiness, hearing loss, ringing in the ears, and trouble sleeping.
In the Family Guy season six episode "Believe it Or Not, Joe's Walking On Air", Stewie Griffin asks Brian Griffin "do you have any Anacin?". A discussion then ensues about whether Anacin is still around. In season eleven's episode "Lois Comes Out of Her Shell" Peter Griffin asks if Anacin is sold at the bar.
- Anadin (similar brand sold in the UK)