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Well, the answer is YES , it is safe to take lithium and rhodeola rosea together , there are no harmful interactions documented between them ..
The only drugs which react with rhodeola rosea are benzodiazepines like lorazepam and clonazepam , etc , SSRI anti depressants like fluoxetine , sertraline , paroxetine , etc..and SNRI anti depressants like venlafaxine and duloxetine , all of these causing drowsiness when used along with rhodiola rosea..
I hope this helps..
Wish you all the best..
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