If President Donald Trump were to close the border, these people's daily lives (and in many cases, their livelihoods), would be deeply affected.
The powerful painkiller has led to a considerable spike in overdoses in some border cities, but users are finding little support in trying to combat the scourge.
As a Honduran man was returned to Mexico under the new plan, questions remained unanswered on both sides of the border.
A group of 150 migrants had approached the border barrier in an attempt to cross, and, after the tear gas was fired, the clash escalated.
Migrants planning to cross, both legally and illegally, say they fear Customs and Border Patrol detention. But because asylum-seekers entering legally are also detained, many still decide to cross the border illegally.
Though the government has opened a large indoor shelter in Tijuana for members of the caravan, around 350 migrants remain in a tent village against the border.
The administration's mass deportations and refusal to take in escapees from disaster may be fueling organized crime in Tijuana and other border towns.