Hey, 1g of fentanyl intravenously would be an enormous overdose. Typically the IV dosages for non-tolerant people would be much smaller than 1 single milligram, 0,001g. Sadly though purity isnt guaranteed in non-pharmaceutical products, the actual purity of street products can widely range and it theoretically isnt even guaranteed to contain actual fentanyl. The only safe method for you to know would be to get it tested professionally, there may be options to get it tested via harm reduction drug checking programs or such things in your region but I dont know. To your question about other drugs: taking other drugs with your opioid can potentiate the respitory depression by alot, other Cns depressants, especially benzodiazepines are shown to be involved in a pretty big part of opioid related deaths. So yes, I think benzodiazepines could be a useful addition to opioid overdoses in general, they are not necessarily essential but if you can aquire them, why not? And besides that I dont really know why people would consider opioid overdoses as a whole to be an "unsafe" suicide method. Opioids not only depress your CNS, they directly dampen your bodies CO2 response via mu-opioid receptors in your brainstem. You dont feel the need to breath because of "low oxygen" directly, you feel the need to breath mainly because of higher levels of CO2 in your bloodstream, your brainstem detects that and automatically "triggers" a breath, exactly that response is reduced by opioids. Opioids are known to be potentially dangerous, especially if taken together with other cns depressants like benzodiazepines, and especially for people who are not used to opioids. I still wouldnt say that opioid overdoses are automatically safe, in my opinion they can be relatively reliable with adequate dosage and in combination with for example benzodiazepines but there are no 100% safe methods. Opioid overdoses can fail and if they fail there would also be a risk of permanent brain damage or so. You can reduce the risk of failure but it wont ever be 0%, no matter the method. Still I wouldnt say that opioid overdoses in general are unreliable, they certainly can be more or less "reliable", even if overdoses as a suicide method in general are statistically more prone to fail. Hope I could help.