I guess since I’m a pharmacist I should talk about drug related topics once in a while.
There is a study that was recently published about the use of acetaminophen (Tylenol) and its use in lower back pain. I don’t have access to the study other than the summary so I can’t make any conclusive remarks about what actually took place but wanted to comment on what was printed.
In this study conducted down under, 1643 people were analyzed for lower back pain and relief with acetaminophen (APAP for the rest of this post). The subjects were randomized into 3 groups; an around the clock dosing, an as needed dosing and placebo. 
The amounts of APAP in the first group were around 3990mg/day, the second group was 4000mg/day and then placebo which had none. They were followed for 3 months but only received 4 weeks of medication. Researchers were looking to see when patients reported relief on a pain scale of 0-1 (on a 1-10 pain scale) for 7 consecutive days.
The results were there was no difference between the 3 groups. The authors concluded that regular use of APAP,
“does not affect recovery time compared with placebo in low-back pain, and question the universal endorsement of paracetamol in this patient group”
Again I don’t have access to the study itself so I can’t delve into specifics, but we can ask a few questions.
Was their a decrease in pain at all and if so how quickly did pain decrease and by how much? What kind of injury caused the back pain in the first place? Was it acute pain or chronic?
To answer the last question it does sound like it was probably more acute pain. Had it been chronic I doubt there’d been any difference in the pain levels over 4 weeks or 4 months, at least not to 0-1.
I can’t answer the first question but I suspect that the answer is the treatment probably did decrease pain, just not to a 0-1 level. I do admit that personally I don’t really respond to APAP for pain, but it does wonders if I have a fever and the opposite is true for Ibuprofen. Some people I’ve talked to respond well to APAP and others don’t.
Since I can only speculate I assume some of the patients did get pain relief while others may not have. The other question though, what caused the pain in the first place, would be relevant as well because if there is an inflammation component that is clinically significant, then APAP might not do so well as it doesn’t help inflammation.
Does that mean that APAP is worthless and shouldn’t be used for lower back pain? Not necessarily. It may be very helpful for some and the only real way to know is to try some. Be aware though that doses much higher than 625mg aren’t more effective than 1000mg.
Taking lots of APAP has the effect of decreasing glutathione in the liver which is one of the body’s main antioxidants. For a short period of time this is likely not a problem, but over weeks and months this could leave you vulnerable to oxidative damage assuming the body isn’t getting enough nutrients in the diet to replenish stores. Fresh meats, veggies like asparagus and spinach, and other foods like garlic contain sulphur compounds which are what the body uses to replenish stores. N-acetyl-cysteine is also used because it’s rapidly converted in the body to glutathione.
This is one of the major problems in the United States as far as drug overdoses are concerned. Around 150 people die every year from APAP overdose.  Those who survive usually end up with sever liver damage and many require transplants. That number of 150 is an average over 10 years from 2001-2010 and they are all accidental.
From 1998-2003 The leading cause of liver failure was APAP overdose.
From 1998-2007 there was an estimated 57,000 ER visits and 26,000 hospitalizations per year due to overdose.
This is pretty serious.
The max recommended dose per day is 3000mg for a healthy adult. Please be aware of medications that may have APAP in them. In other words READ THE LABEL!
Be very careful with children’s doses as well. Sometimes the bottles you get at the pharmacy for an infant will be a different strength that for a bottle you buy at the store that also says infant.
I didn’t mean to turn this into a scare post but it’s important to remember that no medications is benign. We make a big deal about things like weight loss drugs and steroids, and rightly so, but we need not forget the dangers of simple things like APAP.
If you need to use some APAP please don’t feel like I’m discouraging its use. It may be helpful. Just please remember that for something like back pain it’s probably not going to make you feel 100% and that taking more will do nothing for the pain and potentially make it worse if you keep at it for long due to liver problems. NSAIDs like naproxen or ibuprofen may be better suited to the task but talk to your doc or handy pharmacist if you have questions.
1.Efficacy of paracetamol for acute low-back pain: a double-blind, randomised controlled trial Christopher M Williams, Christopher G Maher, Jane Latimer, Andrew J McLachlan, Mark J Hancock, Richard O Day, Chung-Wei Christine Lin
The Lancet 24 July 2014