When the temperature climbs above 24°C (75.2°F), something dangerous happens to people who use drugs: their risk of overdose spikes. It’s not just about feeling hot. It’s about your body breaking down under pressure-heat, dehydration, and drugs working together in ways that can kill. This isn’t theoretical. In New York City, emergency calls for overdoses jumped 22% during heat advisories between 2018 and 2022. In places like Portland and Seattle, where summers used to be mild, overdose deaths during heat domes rose over three times higher than normal. And it’s happening because heat changes how your body handles drugs-often in deadly ways.

Why Heat Makes Overdose More Likely

Heat doesn’t just make you sweaty. It changes your body chemistry. When the temperature rises, your heart works harder just to keep you cool. Add stimulants like cocaine or meth, and your heart rate can jump 30-50% above normal. That’s a recipe for cardiac arrest. Even opioids, which slow breathing, become more dangerous because heat reduces your body’s ability to compensate for low oxygen. Studies show heat can cut respiratory compensation by 12-18%, meaning the line between a safe dose and a fatal one gets dangerously thin.

Dehydration plays a huge role too. Lose just 2% of your body weight in fluids-something that happens easily in hot weather-and drug concentrations in your blood can rise by 15-20%. That’s like taking a bigger dose without realizing it. If you’re using heroin, fentanyl, or even prescription pills, your body isn’t processing them the same way. You might think you’re being careful, but heat is silently increasing your risk.

And it’s not just about the drugs. Many people taking medications for mental health-like antipsychotics or antidepressants-find those drugs become less effective or more toxic in heat. Up to 70% of antipsychotics lose potency above 24°C. That means someone managing schizophrenia or depression might stop feeling stable, turn to other substances to cope, and end up in a worse situation.

Who’s Most at Risk

The people hit hardest aren’t just drug users-they’re people without shelter, without access to water, without support. In the U.S., about 580,000 people experience homelessness on any given night. Nearly 4 in 10 of them have a substance use disorder. They’re sleeping on sidewalks, in cars, or under bridges when the heat hits. No AC. No fan. No way to cool down.

Even those with housing aren’t safe. People living in older apartments without air conditioning, or in neighborhoods where the urban heat island effect raises temperatures 3-5°C above surrounding areas, are at higher risk. A 2023 CDC analysis found that heat-related emergency room visits among people who use drugs were 18-22% higher than average during extreme heat events. Yet, only 12 out of 50 U.S. states have even included substance use in their official heat emergency plans.

And then there’s the silence. People who use drugs often avoid shelters because they’re turned away for being “actively using.” Police in some cities have confiscated cooling supplies from outreach workers. No one talks about this. But it’s killing people.

Robotic outreach workers distributing cooling supplies to vulnerable people under bridges, with heat warnings glowing in the sky.

What You Can Do: Practical Harm Reduction Steps

If you or someone you know uses drugs, here’s what works-not guesswork, not theory, but real, tested strategies:

  1. Reduce your dose by 25-30% when temperatures hit 24°C or higher. Your body isn’t the same in heat. What felt safe last week might be lethal now.
  2. Hydrate like your life depends on it. Drink one cup (8 oz) of cool water every 20 minutes. Not soda. Not energy drinks. Water. This isn’t optional. NYC’s Harm Reduction Coalition cut heat-related overdose calls by 17% just by handing out water and electrolyte packets during outreach.
  3. Avoid mixing drugs with heat. If you’re using stimulants, don’t be outside in direct sun. If you’re using opioids, don’t use alone. Heat makes both more dangerous. Use with someone who has naloxone.
  4. Check your meds. If you’re on antidepressants, antipsychotics, or blood pressure meds, talk to your provider before a heatwave. Some drugs need dose adjustments when it’s hot.
  5. Find cool space. Libraries, community centers, and public transit stations often have AC. Go there. Even two hours of cooling can reset your body’s stress response.

What Communities Should Do

Individual actions save lives-but systemic change saves more. Cities that act differently see better results.

Philadelphia started handing out cooling kits after their 1995 heatwave killed 700 people. By 1999, they’d cut deaths to 100. Their kits included electrolyte packets, misting towels, and info on overdose signs. Today, they distribute over 2,500 annually. Vancouver went further: they opened seven air-conditioned respite centers next to supervised consumption sites. During the 2021 heat dome, they reduced heat-related overdose deaths by 34%.

Maricopa County in Arizona trained volunteers to check on people living outdoors. During the 2022 heat season, they made over 12,000 wellness checks and intervened in 287 overdoses-using naloxone, water, and shade.

The CDC now recommends every city have a Heat and Health Risk Factor Screening Questionnaire for healthcare providers. It asks about housing, medication use, drug history, and access to water. Simple questions. Big impact.

And now, federal funding is starting to catch up. In 2023, the U.S. government allocated $50 million to help states build overdose prevention into heat emergency plans. By December 2025, every state must include it-or risk losing funding.

A massive air-conditioned respite center rising from the city, spraying mist over people on the pavement with glowing green energy panels.

The Bigger Picture: Climate Change Is Making This Worse

By 2050, climate models predict 20-30 more days each year where temperatures exceed the 24°C overdose risk threshold. That’s not a future problem. It’s already happening. Places like Aberdeen, Scotland, which used to have mild summers, saw record highs in 2022. What was rare is becoming normal.

Even the way drugs are processed in your body is changing. New research from the NIH suggests heat alters gut bacteria by 15-20%, which could affect how drugs are absorbed. We don’t fully understand it yet-but we know enough to act now.

Heatwaves aren’t just weather events. They’re public health emergencies. And people who use drugs are among the most vulnerable. Ignoring this link isn’t negligence-it’s deadly.

What to Do Right Now

Don’t wait for a policy change. Don’t wait for someone else to act.

  • If you use drugs: cut your dose. Drink water. Find shade. Use with someone who has naloxone.
  • If you know someone who uses drugs: ask if they’re okay. Bring them water. Help them find a cool place. Don’t judge. Just care.
  • If you work in healthcare or outreach: start asking about heat exposure. Use the CHILL’D-Out screening tool. Push your agency to stock water, electrolytes, and cooling packs.
  • If you’re part of a community group: organize a cooling station. Partner with local harm reduction groups. Distribute supplies. Talk to city council.

There’s no magic solution. But there are simple, proven steps. And they work. People are alive today because someone remembered to offer water. Because someone didn’t turn them away. Because someone cared enough to act.

Can heat really cause an overdose even if I don’t use more drugs?

Yes. Heat changes how your body processes drugs. Dehydration concentrates drugs in your blood, and heat reduces your body’s ability to handle their effects. You might be using the same amount, but your body is under more stress-making a previously safe dose dangerous.

Why are people who use drugs more affected by heat than others?

Many have co-occurring health conditions like heart disease or mental illness, which are worsened by heat. Many also lack access to air-conditioned spaces, clean water, or medical care. Some medications they take interact dangerously with heat. And substance use itself can impair judgment and thermoregulation-making it harder to recognize danger.

Is naloxone still effective during a heatwave?

Yes. Naloxone works the same way regardless of temperature. But heat can make overdoses happen faster and more severely, so having naloxone on hand and knowing how to use it is even more critical. Always carry it during hot weather, and make sure others around you know where it is.

What if I’m turned away from shelters during a heatwave?

Many shelters still have policies that exclude people actively using drugs. That’s changing, but slowly. In the meantime, look for public spaces with AC-libraries, malls, transit hubs. Some cities have opened special cooling centers for vulnerable populations. Reach out to local harm reduction groups-they often have networks to connect people with safe places to cool down.

Are there specific drugs that are more dangerous in heat?

Cocaine and methamphetamine are the most strongly linked to heat-related overdose deaths because they raise heart rate and body temperature. Opioids are dangerous too-heat reduces breathing capacity, making overdose more likely. Even alcohol and benzodiazepines can increase dehydration and impair judgment. No drug is safe in extreme heat without precautions.