SNRI VS. SSRI - Advice Needed

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Splash151

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Good Afternoon -

I am currently on 150mg of Effexor XR for treatment of Complex Post Traumatic Stress Disorder. I have been on it for 10 months after using Cymbalta prior for 2 years and then moving overseas where it was no longer available.

In November, I had completed a dive physical at Dan Egypt in Sharm-El-Sheikh in hopes to be cleared for my Divemaster and Tec 40 classes, and was made aware of the significant seizure level of this medication combined with Trimix/higher oxygen gas concentrations at depth.

This was news to me, as I have been cleared to dive having been on this medication in the past.

In a nutshell, I was told there was no way I would be cleared to Tech dive safely while on this drug, and especially at my current dose as the risk was too great. I was cleared for my Divemaster but was informed it was not a smart decision and was told that SSRIs were a safer bet than SNRIs at depth.

I am in the middle of preparing (e-learning) for my Divemaster which is to be completed this summer as soon as the airports reopen in Oman and I can get to Egypt. I am also supposed to spend the rest of the summer doing research on Great Whites in Cape Town. A lot of moving, and a lot of time underwater.

I had no symptoms other than increased euphoria at depth in the Red Sea at around 80-90ft, and honestly do not know if that was because of medication, or simply because the diving was the best of my life. I was as cool as a cucumber.

Switching medications is not a short journey and is not without challenges. While my end goal is to be completely off medications for trauma, I am not at that point in my life/personal therapy yet. Diving has been my peace through it all. I am working on lowering my dose to 75mg of Effexor to lower the risk.

Two Questions:

1. Does anyone have advice or is willing to share substantiated evidence that supports a higher level of safety on SNRIs vs SSRIs at depth? (i.e making a medication switch on my timeline a smart idea)


2. I will not be pursuing technical diving while on an SNRI, as it was clear from our conversation that it was ill-advised but I am indeed curious if it would be safe to do so on an SSRI?


Thank you very much for your time and responses!
 

fishead6

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Splash,

Speaking generically, we all have a seizure threshold. That is the amount nervous activity which would trigger a seizure. Certain things can lower the threshold and cause a seizure. Both SNRI and SSRI meds are known to lower the threshold. In theory, if you take these meds, and you increase your O2 sat close to limits, you MIGHT have a seizure sooner than someone not on meds. That being said, I medically certify quite a few divers that are on meds like you. PADI lists meds like yours as "relative risk."
Your agency's regs may be different just due to the depths and times you might be diving. BTW the dose you describe is not excessive by today's psychiatric standards. As I know it, the risk of SNRI and SSRI would be the same, so if you are doing well on Effexor, there is no advantage to changing to an SSRI. My 2 cents. Good luck.
 

Duke Dive Medicine

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Good Afternoon -

I am currently on 150mg of Effexor XR for treatment of Complex Post Traumatic Stress Disorder. I have been on it for 10 months after using Cymbalta prior for 2 years and then moving overseas where it was no longer available.

In November, I had completed a dive physical at Dan Egypt in Sharm-El-Sheikh in hopes to be cleared for my Divemaster and Tec 40 classes, and was made aware of the significant seizure level of this medication combined with Trimix/higher oxygen gas concentrations at depth.

This was news to me, as I have been cleared to dive having been on this medication in the past.

In a nutshell, I was told there was no way I would be cleared to Tech dive safely while on this drug, and especially at my current dose as the risk was too great. I was cleared for my Divemaster but was informed it was not a smart decision and was told that SSRIs were a safer bet than SNRIs at depth.

I am in the middle of preparing (e-learning) for my Divemaster which is to be completed this summer as soon as the airports reopen in Oman and I can get to Egypt. I am also supposed to spend the rest of the summer doing research on Great Whites in Cape Town. A lot of moving, and a lot of time underwater.

I had no symptoms other than increased euphoria at depth in the Red Sea at around 80-90ft, and honestly do not know if that was because of medication, or simply because the diving was the best of my life. I was as cool as a cucumber.

Switching medications is not a short journey and is not without challenges. While my end goal is to be completely off medications for trauma, I am not at that point in my life/personal therapy yet. Diving has been my peace through it all. I am working on lowering my dose to 75mg of Effexor to lower the risk.

Two Questions:

1. Does anyone have advice or is willing to share substantiated evidence that supports a higher level of safety on SNRIs vs SSRIs at depth? (i.e making a medication switch on my timeline a smart idea)


2. I will not be pursuing technical diving while on an SNRI, as it was clear from our conversation that it was ill-advised but I am indeed curious if it would be safe to do so on an SSRI?


Thank you very much for your time and responses!

Hi @Splash151 ,

There is no scientific literature that supports use of one over the other in divers, and I'm not aware of any literature that specifically states that SNRIs present a higher risk of seizure when combined with higher partial pressures of O2. Some literature I found in a brief search is linked below. The first one is specifically related to divers. You may not be able to get the full text through the link, so I'll paste the relevant part here:

"SEIZURES
An antidepressant overdose may induce seizures. At a normal dose of clomipramine, and more so with bupropion, there is an increased risk of the occurrence of convulsions.[ 4] One review of the newer antidepressants considered the risk generally to not be very different from the incidence of first seizure in the general population, whereas the risk with tricyclic antidepressants at effective therapeutic doses is relatively high.[ 5] Ten years later a follow-up study of 151,005 depressed patients showed that the current use of SSRIs or SNRIs is associated with a twofold increased risk of first-time seizure compared with non-use, while current use of tricyclic antidepressants (mostly low dose) is not associated with seizures.[ 6] Treatment initiation in SSRI and SNRI users is associated with a higher risk of seizures than longer-term treatment.[ 6] However an analysis of 238,963 British patients diagnosed with depression led to the conclusion that risk of seizures is significantly increased for all classes of antidepressants.[ 7] There are no data on whether these agents increase risks of or sensitivity to central nervous system oxygen toxicity." (Querido, 2017, p 254)

The next three are the references from the Querido paper, annotated with the reference number in the paragraph above. Reference (7), the Hill paper, may be where the concern over the venlafaxine came from, but as you'll read, the evidence is mixed.

Diving and antidepressants
(5) Antidepressants and seizures: emphasis on newer agents and clinical implications. - PubMed - NCBI
(6) Risk of Seizures Associated with Antidepressant Use in Patients with Depressive Disorder: Follow-up Study with a Nested Case-Control Analysis Using... - PubMed - NCBI
(7) Antidepressant use and risk of epilepsy and seizures in people aged 20 to 64 years: cohort study using a primary care database. - PubMed - NCBI

Another paper on SNRIs, SSRIs and seizure:
Seizures during antidepressant treatment in psychiatric inpatients--results from the transnational pharmacovigilance project "Arzneimittelsicherhei... - PubMed - NCBI

I hope this helps give you a little background. Maybe you can use the information here to formulate some follow-up questions for your physician. As you probably already know, the risk of CNS O2 toxicity is dependent on the inspired partial pressure of O2, not the depth per se. You can reach a dangerously high inspired partial pressure of O2 at relatively shallow depths on nitrox.

Best regards,
DDM
 

judyo1

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Both SSRIs and SNRIs do lower seizure threshold. I have not seent this apply in real life - more of a theoretical risk.
150mg od of venlafaxine is not a high dose. If the venlafaxine works, stay on it and don't push your limits in terms of MOD.
I would imagine you'd be a far greater risk diving with unmanaged anxiety / depression / PTSD.
 
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