Thought I’d share a quickie from a reader, who asked if Suboxone or buprenorphine were affecting his vision.
One thing I’ve noticed when I’m not on any drugs is my pupils are fairly large. For some reason after I stopped the Vicodin, my vision got really blurry. I’ve worn glasses most of my life, nearsighted but even with the glasses, they were blurry. Then when I started taking Subutex, things got sharp again. I didn’t change my prescription or anything. It’s got to have something to so with opiates or drugs like them.
The vision issue is fairly straightforward. The smaller the pupils (the ‘aperture’), the sharper the vision—a phenomenon that results from basic optics. All opioids except Demerol (meperidine) cause our pupils to constrict (meperidine has an ‘anticholinergic’ effect that dilates the pupils. The drug has other anticholinergic effects that doctors often remember using a mnemonic: Dry as a bone, red as a beet, mad as a hatter, and blind as a bat). But again, the actions of most opioids make pupils smaller, and therefore vision becomes sharper. The effect is less helpful during low-light conditions thought, when smaller pupils results in less light reaching the retina, which reduces or prevents color vision and makes images harder to define.
Vicodin likely improved your vision by constricting your pupils, as long as you were not in withdrawal, and I’m just assuming you didn’t notice the vision change during withdrawal because of all the other things to worry about!
Why should buprenorphine cause pupillary constriction through an opioid-mediated effect, though, if we accept that people on buprenorphine become fully tolerant to the mu opioid effects of the drug? There may be some residual opioid effects even during full tolerance, but there is another explanation that I think is more interesting. When people take a standard tab of film of 8 mg of buprenorphine or Suboxone, respectively, they absorb 25% of the buprenorphine into the bloodstream, and swallow the other 6 mg of drug. That swallowed buprenorphine is absorbed at the small intestine and converted, at the liver, to norbuprenorphine. Essentially no buprenorphine makes it past the liver (a phenomenon called the ‘first pass effect’ of buprenorphine), but 6 mg of norbuprenorphine DOES enter the general circulation.
We tend to ignore norbuprenorphine except for forensic or quantitative urine drug testing, because norbuprenorphine does not cross the blood brain barrier in humans. But norbuprenorphine does have opioid effects elsewhere in the body, including at the pupil and at the intestine. The effects of norbuprenorphine are NOT subject to a ceiling effect. It is worth noting that the new buprenorphine drug Bunavail has lower incidence of constipation, possibly because of the reduced exposure to norbuprenorphine (2 mg of buprenorphine is swallowed with a standard dose of Bunavail, compared to 6 mg with Suboxone film). What else does all that norbuprenorphine do? Is night vision better with Bunavail than with Suboxone Film? Where is a good grad student when you need one?
(addendum for the real scientists out there… I realize I’m out on a limb. But that’s the most enjoyable part about having a blog– I just get to wonder about things!)