The 18-year-old was taken to hospital after collapsing in a street in Bexley, late on Saturday. He died two hours later.
The Metropolitan Police said he was believed to have been drinking alcohol as well as ingesting legal high nitrous oxide, also known as laughing gas.
Seventeen people in the UK died between 2006 and 2012 after taking the drug.
The teenager's next of kin have been informed.
"At this stage the death is being treated as unexplained pending the findings of the post-mortem," the BBC quoted a Met spokesman as saying.
The gas - inhaled using a balloon - can make people feel relaxed, euphoric and giggly, which has led to its nickname. But abusing nitrous oxide can lead to oxygen deprivation, resulting in loss of blood pressure, fainting and even heart attacks.
It is not illegal to be in possession of the gas, although it is prohibited from being sold in England and Wales to under-18s if there is a risk they will inhale it.
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
