Depending on whether you're a glass-half-empty or glass-half-full kind of person, the current international state of blood donation could tell one of two stories.

An optimist might conclude from the available statistics that the world is good and benevolent: Indeed, 78 countries, most of which are middle to high-income, gather more than 90% of their blood supply from unpaid, voluntary donors. 56 of those countries gather 100% of their supply from unpaid, voluntary donors.

Although that may seem like a lot of goodwill, it's only a small fraction of what it could be - according to the WHO, 90% of eligible blood donors don't donate.

A pessimist might further conclude that these statistics tell a predictable story of income inequality: Indeed, the median annual donations per blood center, as compared to 23,000 in high-income countries like the United States and Germany, is around 1,000 in low-income countries like Pakistan and Zambia, 4,000 in lower-middle-income countries like Egypt, and 9,000 in upper-middle-income countries like Turkey and Belize.

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This means that if you need an urgent blood transfusion, you're far more likely to receive one - with clean, safe blood - in a rich country than a poor one.

In poor countries in East and Southern Africa, where AIDS and HIV diagnoses affect more than 25% of the population, this is a problem. It is also a problem in cities such as Pune, India, where natural disasters and scorching temperatures sparking fears of dehydration are keeping donors from going to the blood bank.

And although most industrialized countries get by, many still run low on blood. Ireland, for example, experienced a nationwide blood shortage last year, with over 620 people waiting for a bed at a local hospital.

Last month, the American Red Cross issued a "critical need” for Type O blood donations in US clinics, the most common blood type in the world.

The pessimist may be winning this debate, but he doesn't have to. If you've ever considered donating blood but decided against it because you thought marijauna smokers weren't allowed to, you're in luck. Here are all your questions about blood donation, answered.

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Who can and can't donate blood?

According to the WHO, in Europe, the standard age limits are 18-65, with some leeway. If you are younger and want to donate, you can in some cases with parental consent. These age limits are continually stretched due to blood shortages, according to the organization.

Aside from age, if you are part of any of the following risk groups, you can't donate:

• Bi- and homosexual men who have had sexual contact with other men.
• People who have injected drugs, along with drug addicts.
• Prisoners, sex tourists and prostitutes.
• People infected with HIV, AIDs and syphilis.
• People who have different sexual partners very frequently.
• People who have had sex with someone in any of the listed risk groups in the past four months.

Which types are the most common? Least common?

In most places, the most common blood type is O positive, then A positive. The least common is AB negative. Logically, O negative is the most in-demand blood type, as it can be given to anyone. That said, this is different from country to country and in different ethnic groups.

Can I donate blood if I have tattoos/piercings/am gay?

If you received your tattoo or piercing within the past four months, you are not allowed to donate. Otherwise, you're fine. In Germany, If you're a gay woman who has never had sex with a gay man, you are fine, but if you are a gay man who has had sex with a man, you can't donate. If you are a straight man but have had sex with a man, you can't donate. If you are a woman who has had sex with a gay man, you can't donate.

Some countries such as Germany, where full bans exist, are pushing to change the laws to allow gay men to donate blood, with LGBTQ organizations calling them discriminatory and outdated. In the US and the United Kingdom, for example, gay men are allowed to donate if they have abstained from sex with men for a specific amount of time.

The policy stems from the AIDS epidemic in the 1980s, when the virus was spread to the US and Europe from Africa and infiltrated pockets of gay populations, specifically in New York City and Los Angeles. Gay men are still at the highest statistical risk of contracting HIV-AIDS.

Can I donate blood if I smoke cigarettes or weed and drink alcohol?

Yes, just don't come to your appointment high or drunk. Clinics don't test blood samples for cannabis, alcohol or cigarettes, but if you are high or drunk, you will be turned away.

Who's getting my blood?

Anyone could receive your blood. Once it has been tested for infectious diseases such as HIV-AIDS and syphilis, it will be transferred to a hospital where it will be used for blood transfusions, which can be given to victims of accidents such as car crashes, cancer patients, people undergoing surgeries, childbirth and to people with blood disorders. 

What should I do beforehand?

Before donating, make sure you've eaten a decent meal and drunk around a liter to a liter and a half of water. When I donated, the doctor who I did my pre-consultation with told me to drink a few more cups of water because I told him I'd probably only drunk half a liter that day.

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Can I drink alcohol afterwards?

When I asked my doctor about this, he told me that a beer wouldn't hurt me, but that I shouldn't go wild that night. Naturally, for the sake of journalism, I drank a beer that evening to see what would happen. I'd read in some Reddit chat rooms that university students sometimes give blood before partying so they could get drunk quicker.

The beer was perhaps slightly stronger than normal, but nothing particularly noteworthy.

Am I going to get paid?

It depends on where you go. If you go somewhere like the German Red Cross or American Red Cross, you will not get paid, but there are private companies in Germany and the US where you could be. In Britain and Australia, blood donation is entirely unpaid and voluntary.

Some people — and organizations such as the WHO — say it is unethical to be paid for blood donations, arguing the model preys on the poor and could make donations more unsafe. Germany argues that it is compensating people for their time —  if people know they will lose two hours of unpaid work, they may be less inclined to donate.

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What about plasma?

Whole blood is the most common and easiest form of blood to donate. The process takes less than 20 minutes. You have to wait 8 weeks between each whole blood donation to allow your red blood cells to replenish.

You can donate plasma more frequently, because your plasma replenishes itself after 5 days, but the process takes much longer than regular blood donation, often lasting up to 2 hours. The process consists of plasma being separated from red blood cells. The plasma is extracted and the red blood cells are returned to your body.

Okay, but what is it actually like? I'm nervous.

I donated blood for the first time for this article. As a fairly anxious person, I was certain something would go wrong. Everything, of course, went very well.

When I got to the clinic, they asked for my passport and proof of residence and had me fill out some general forms. They weighed me, tested my iron levels and checked my blood pressure. 

Afterwards I had a 20-minute consultation with a nurse because it was my first time donating. We discussed my drug habits and health and sexual history.

Most of the people in the waiting room seemed quite young, which surprised me. My nurse said it was because the clinic pays people to donate, and some students donate so much blood and plasma that they consider it a side job.

During the donation process, I sat in a reclining chair and my nurse made small talk with me as she prepared the syringe. I told her I was nervous and she ordered another nurse to come hold my hand and distract me while the needle was inserted into my arm. She tried practicing her English with me, much to the delight of her colleagues, and I was soon surrounded by a flock of smiling nurses clothed in jackets reading "Blood Angel" on the back.

Is this what heaven feels like? I asked myself.

Then the needle went in. 

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My hand felt kind of staticky after the initial injection, like it was asleep, and I felt mildly dizzy, but I think the dizziness was nerve-induced. After the primary sting, I didn't feel much pain.

It didn't hurt when she removed the needle after about 10 minutes. 

I walked home later without any problems. I didn't notice any real difference that evening aside from being perhaps a bit more tired than normal. Otherwise, the donation had very little effect on my body.