Well it all depends who you listen to.
I'll tell you the absolute worst I've heard, some from half-assed medical studies.
* WHITE OUTS - I don't really see this as a health problem, but you mentioned blackouts in your question. It only happens when you smoke WAAYY too much for you to handle, kinda like passing out drunk
* NAUSEA - first time, quite a few people say they feel ill, or are physically sick. This is a lot more common if you're drinking alcohol as well as smoking weed. Remember kids, when mixing weed and alcohol, take half measures of both!
LONG TERM PHYSICAL
* CANCER (if you're smoking with tobacco) - If you roll a joint, or mix with tobacco, then the risk of cancer is still there. Weed itself doesn't show any evidence of causing cancer. Smoking with a vape is the healthiest way. (Vapourisor, bit expensive for all the kiddies, but a good investment if you're a proper stoner)
* BRONCHITIS / BAD COUGHS (smokers coughs) - You ARE burning something and inhaling the fumes, it's bound to irritate your bronchial tubes (things in your lungs that produce mucus). This means that you MAY get bronchitis, which is a ***** of an illness - basically makes you cough up A LOT of phloem. This is why you often see smokers spit.
* There's an old stoner rumour going 'round that if you eat the stems of weed you become infertile - it's utter crap and doesn't even make sense. Though I wouldn't suggest eating stems of weed anyway, you won't get anything from it. There are actual things you can do with the stems (make reject hash, for example, but thats a bit of a pain. If you stick a lot of them in vodka, and leave it to chill for a couple weeks, it adds a great kick to the drink).
LONG TERM MENTAL - These aren't necessarily true, but there is some evidence. If you want to know more about the psychological affects of marijuana, google it.
* SHORT TERM MEMORY LOSS - not much I can say about this one
* PARANOIA - anybody who watches Jeremy Kyle knows this, "THE TOP SIDE EFFECT OF CANNABIS USAGE IS PARANOIA YOU COUNCIL HOUSE SCUUUMM".
* SLOWING OF REACTION TIMES - My science teacher told me this one many moons ago. This was a long time ago and I've never googled it too see if it's true, but he told me that marijuana works by making your body produce excess serotonin. Serotonin is used by synapses, the things that send electrical pulses all round your body, they control how fast your reactions are. e.g. say you put your hand in a fire, they dictate how long it'd take for an impulse saying "AH TAKE ME OUT" from your hand to your brain. Anyway, Mr Gilbert said to me that excess serotonin means that the synapses get somewhat "clogged" meaning that it takes more effort for them to work, therefore it takes longer
* SCHIZOPHRENIA - NOT PROPERLY PROVEN. I think there was one medical study looking into the minds of long term marijuana users and it showed a mild correlation between long term marijuana usage and schizophrenia. But Mr Gilbert wasn't a totally useless teacher, he also taught me that correlation does not mean causation, it could be something else entirely.
LESSENING THE RISKS
You can say you're asking for "research" but you're really weighing up the pros and cons of accepting the spaced-out-kid-down-the-road's invitation of going into his shed and getting high. I say go for it; I believe kids these days would say "YOLO" to this situation.
* DONT OVERDO IT - the spaced out kid has a higher tolerance than you, don't try to keep up with him to be "cool". You'll end up doing the opposite when you pass out in a puddle of your own vomit.
* FOR GOD'S TAKE DON'T USE TRAIN TICKETS AS ROACH - the ink on train tickets is HIGHLY HIGHLY carcinogenic and its a pointless risk.
* WHERE POSSIBLE, USE A BONG/VAPE - Far healthier.
* DON'T END UP SMOKING £100 A DAY - chances are, you'll go a bit weird in the head