Check whether a plugin is active.

Only plugins installed in the plugins/ folder can be active.

Plugins in the mu-plugins/ folder can’t be “activated,” so this function will return false for those plugins.

Signature

is_plugin_active( $plugin )
plugin
 (string) Path to the main plugin file from plugins directory.

Return

(boolean) True, if in the active plugins list. False, not in the list.

Source

function is_plugin_active( $plugin ) {
	return in_array( $plugin, (array) get_option( 'active_plugins', array() ) ) || is_plugin_active_for_network( $plugin );
}
WP Trac GitHub

Link here