Serotonin has general constrictive and inflammatory effects in the body, including the brain. It constricts your personality and gives you tunnel vision about the future. How exciting does a gray determined future look like? Not very great.

Dopamine on the other hand is involved with excitement, motivation, drive, life enjoyment, pleasure, mental sharpness, openmindedness and much more.

Serotonin is known to contribute to apathy and anhedonia amongst many other even worse side effects, such as blood clotting, PSSD, worsened suicide risk, enhanced viral infections and the inflammatory response, asthma and COPD, PTSD, etc.

And it’s not the serotonin to dopamine ratio, but serotonin in general that causes problems. If serotonin remains too high long term, then it might contribute to long term dysfunction of the dopaminergic system.

SSRI's are a big failure for depression and that’s why many other alternatives are being explored at the moment, such as anti-inflammatories, ketamine, Agomelatine, adamantane derivatives (Bromantane, memantine, adamantine, etc.), dopaminergics, noradrenaline uptake inhibitors, etc.

But the thing is, the more neurotransmitters and receptors are being modulated at the same time, the less likely things will turn out to work.

Other compounds that restore proper energy metabolism, such as methylene blue, niacinamide, succinic acid, magnesium, vitamin B1, creatine, etc., all have anti-depressant effects without the possibility of dopamine antagonism and apathy/anhedonia.