I'm not a healthcare professional.
Depression is an umbrella term and it covers a wide range of different things, and a wide range of severity. At its most severe depression is a fatal illness. It is safe[1] to ask people if they've considered suicide. If people have suicidal thoughts this is a medical emergency.
If someone has situational depression they may need support to help fix the situation or to cope with it if it's not fixable.
If someone has a depression that doesn't appear to have a cause there's a variety of things that people try. These don't work for everyone. Some of them have worse evidence bases.
1) Lifestyle changes. These include sleep hygiene (good evidence), exercise (not great evidence but there is sign of some benefit), food (not great evidence), and cutting down on alcohol (good evidence). MH professionals have a concept called "activation". As depression takes hold the person loses track of their routines and habits, and they enter a cycle of not doing anything because they're in a low mood, and being in a low mood because they don't do anything. Activation is part of treatment and it involves gradually building up your routines as treatment progresses.
2) Meds. Meds can be split into roughly 5 groups: Tricyclics (avoid if you can), MAOIs (only used for severe treatment resistant depression), SSRIs/SSNIs/NASAs/etc (reasonable evidence base, some people need to cycle through a few to find one that works, some people have unpleasant discontinuation effects), supplements (St John's Wort etc. I'd avoid these unless you're sure the product is good quality, but if you're taking something it's probably better to take real meds), and then things like ketamine which is new and so will be difficult to get for a while. (It's probably useful, it's probably not the miracle drug they claim).
3) Talking therapy. The one with the best evidence base is cognitive behaviour therapy. This is a time-limited therapy with a maximum of 21 weeks, but you can do less if you need less. It's talking about your emotions and thoughts today. It doesn't go into your past. This means it's less suitable for people with trauma in their history.
When we look at effectiveness, meds are effective for about 60% of the people who try them. CBT is effective for about 60% of the people who try it (although that figure is lower because it's mostly based on the English implementation of CBT which can be only 6 weeks over the telephone instead of up to 21 weeks face to face).
Talking to a professional is a good idea. Psychiatrists usually do diagnosis and medication, although some do talking therapy too. Psychologists usually do either diagnosis or formulation, and will offer a range of talking therapies, and sometimes a bit of a mix to suit. It would be good if your friend had a clear ideas about what they wanted to focus on in treatment and what their goals are, although obviously that can be tricky if their thinking is muddled.
You mentioned drug use. Some people do report remarkable, life-changing, experiences after using psychedelics. But it's important to remember that a few people have bad experiences, and some people are harmed. In general (at least in the UK) people who take psychedelics have a good reputation for harm minimisation and responsible drug use, so if you can find a forum you're likely to get good advice and advice that you can check against other sources.
In England this is the guidance for treatment that patients can expect: https://www.nice.org.uk/guidance/cg90
Hope things pick up a bit for your friend.
[1] A bit more about suicide. Asking people is safe; get people to make a safety plan; get them to seek help.
The Zero Suicide Alliance have a 20-30 minute free training video here: https://www.zerosuicidealliance.com/training
https://themighty.com/2020/08/study-safe-to-ask-about-suicid...
https://www.prevent-suicide.org.uk/