import re


def is_weight(word):
    """
    is_weight()

    Purpose: Checks if word is a weight.

    @param word. A string.
    @return      the matched object if it is a weight, otherwise None.

    >>> is_weight('1mg') is not None
    True
    >>> is_weight('10 g') is not None
    True
    >>> is_weight('78 mcg') is not None
    True
    >>> is_weight('10000 milligrams') is not None
    True
    >>> is_weight('14 grams') is not None
    True
    >>> is_weight('-10 g') is not None
    False
    >>> is_weight('grams') is not None
    True
    """
    regex = r"^[0-9]*( )?(mg|g|mcg|milligrams|grams)$"
    return re.search(regex, word)