Overdose deaths in the U.S. rose an estimated 19 percent between 2015 and 2016, the largest-ever spike, the New York Times recently reported. 

In fact, overdoses are now the leading cause of death of Americans under the age of 50, and the opioid crisis keeps getting worse, spurring many citizens to demand Washington do more to stop it.

Here is a look at the drugs taking the most lives, according to a 2014 report from the Centers for Disease Control and Prevention's National Center for Health Statistics (NCHS).

Diazepam, first marketed as Valium, is a prescription drug used to reduce anxiety. 

The drug is considered habit-forming, and should not be taken for more than four months. It can be deadly if mixed with alcohol or other drugs.

Overdose symptoms include drowsiness, loss of balance, muscle weakness, fainting and death. 

The CDC reported that 1,729 people died from diazepam overdoses in 2014.

Artist Thomas Kinkade died from a mix of alcohol and diazepam in 2012. Actor Heath Ledger died from a mix of prescription medications including diazepam in 2008. 

Hydrocodone, used in Vicodin, is an opioid used to treat severe pain. 

Like other narcotics, hydrocodone is addictive. Taking too much can cause slowed heart rate, muscle weakness and fainting.

In 2014, 3,274 people died of hydrocodone overdoses, according to the CDC. 

Here, Patricia Reynolds-Udell poses for a 2012 profile about hydrocodone addicts. She died that same year. 

Methadone is a type of opioid used to reduce withdrawal symptoms in people trying to curb an addiction to heroin and related drugs. It is often used at clinics and treatment centers. 

While methadone doesn't produce the high that other opioids do, it can still be habit-forming, and overdose symptoms are similar to those of other narcotics. 

The CDC reported that 3,495 people died of methadone overdoses in 2014. 

Methamphetamine, or meth, is a stimulant used in the prescription drug Desoxyn. But it's often sold illegally.

Normal meth is a pill or powder, but crystal meth resembles glass fragments. The drug can be swallowed, snorted, injected, or smoked.

Meth is highly addictive and causes extreme energy and decreased appetite. Overdose side effects include convulsions, cardiovascular collapse and death. 

In 2014, 3,728 people died from methamphetamine overdoses, according to the CDC. 

Morphine is an opioid and can trigger the same side effects as other narcotics. 

Here, a baby whose mother had abused prescription painkillers or anti-anxiety medicines while pregnant receives a dose of morphine from medical staff.

In 2014, 4,022 people died of morphine overdoses, according to the CDC.

The primary source of morphine is the straw of the opium poppy, pictured here. 

Fentanyl is a synthetic opioid prescribed as patches or lozenges to treat severe pain.

It is also illegally sold through drug markets and mixed with heroin or cocaine without the buyer's knowledge to increase those drugs' euphoric effects. Because fentanyl can be 50 times more potent than heroin, unsuspecting users are at high risk of an overdose.

According to the CDC, 4,200 people died of fentanyl overdoses in 2014. Overdose deaths involving synthetic opioids other than methadone, including fentanyl, increased by 72 percent from 2014 to 2015, according to the CDC. 

In 2016, music legend Prince died of an accidental fentanyl overdose. Officials later determined the drugs that killed him were obtained illegally.

In 2014, 4,217 people died of alprazolam overdoses, according to the CDC. 

Oxycodone is a prescription opioid. Percocet, Tylox, Percodan, and OxyContin all contain oxycodone.

It is used by some addicts to achieve a high similar to a heroin rush. Overdose symptoms are similar to those of other narcotics.  

The CDC reported that 5,417 died of oxycodone deaths in 2014.

Here, Steven Steiner Sr. sits with a picture of his son Stevie, who died of an OxyContin overdose in January 2001. Steiner has since founded an organization called DAMMADD (Dads and Mad Moms Against Drug Dealers).

Cocaine is a highly addictive stimulant. When sold illegally, cocaine looks like a fine, white crystal powder. It is usually snorted, smoked or injected.

Overdose side effects include hallucinations, paranoid delusions, hyperthermia, elevated blood pressure, arrhythmias (irregular heart rhythm) and death. 

According to the CDC, 5,856 people died of cocaine overdoses in 2014. 

Heroin, which can be injected, smoked or snorted, is an illegal opioid.

Many users take it with other drugs or alcohol. Heroin overdoses lead to shallow breathing, comas and death. 

Risks from injecting the drug with unclean needles include viral infections like HIV and bacterial infections.

Between 2000 and 2015, the rate of heroin-related overdose deaths nearly quadrupled, according to the CDC, and the numbers continue to rise.

Nearly 11,000 people died from a heroin overdose in 2014. Nearly 13,000 died from a heroin overdose in 2015.