Venlafaxine and Lamotrigine, Should dose change since I lost weight?

[GenTheHen]

I am 24 years old, after severe depression/mania/psychosis from age 12-20 I tried many Antidepressants/mood stabilizers/anti psychotics and even ECT(with no effect), I finally got the right balance of 225mg of Venlafaxine in the morning(8am) and 300mg of Lamotrigine at night(8pm). I have been stable with limited mania/depression and no psychotic features for 6 years now. I weighed 97kg when I first started this dose of Venlafaxine and Lamotrigine 6 years ago, however over the last 11months I have slowly lost weight through exercise and healthy eating/portions. I have noticed as this was happening in hindsight I was/am feeling more tired, I find it very hard to wake up in the morning and just generally tired(but not in a depressed way) Also my heart rate during exercising has been pretty consistent at 170 beats a minute but I just took it again these last couple of weeks and it has been around 200 beats a minute and afterwards takes about 10-20minutes for it to start to go back to normal range. Feel quite like crap until it calms back down. Could this be due to the amount of medicine I take and my weight being smaller(75kgs) ? and causing side effects now cause the dose is too high? Should I talk to my doctor about possibly reducing it a little?
What are other peoples experience with weight loss and these medicines? I don't want to take just my doctors word I want to make sure I fully know as it is my decision not just his.

Also I have no physical illnesses, generally healthy according to GP

[GenTheHen]

I have just seen my GP, normal blood results, thyroids normal. all that stuff.

These new symptoms have been happening gradually, it wasn't like one day I woke up did exercise and heart beat was fast, it slowly got faster to a point where I consciously noticed it.

I should have said, I have had similar effects in the past related to doses of other medications which I suppose Is why I think it's that. But am interested to hear if anyone else has and how they went?

[Anonymouse88]

I would get your physical health checked first.  Extra fat, to my knowledge, does not have a huge effect on medication metabolism, at least not as much as more muscle mass does.  You're on a perfectly normal dose of both meds, not some crazy high dose for large size.  Given that your weight loss has been fairly steady and not sudden, but your heart rate increase and discomfort during exercise was (or was more sudden than the weight loss), I'd say it's more likely a physical problem and not related to the meds.  With the healthy eating and exercise (and go you for doing it!), your heart rate while exercising should be getting lower, not higher, and your resting heart rate should be lower than it was.

When was the last time you got things like your thyroid checked?  Depressive symptoms can be caused by a number of organic diseases or conditions, and just because you have a primary mental health problem doesn't mean that one of those other things couldn't happen.  You should definitely speak with your doctor(s) about this, but don't be too quick to blame it on the meds.